Calcium oxide. Physical, thermal and chemical properties

Structural formula

True, empirical, or gross formula: CCaO3

Chemical composition of calcium carbonate

Molecular weight: 100.088

Calcium carbonate (calcium carbonate) is an inorganic chemical compound of carbonic acid and calcium. Chemical formula - CaCO 3. It occurs in nature in the form of minerals - calcite, aragonite and vaterite, is the main component of limestone, marble, chalk, and is part of egg shells. Insoluble in water and ethanol. Registered as white food coloring (E170).

Application

Used as white food coloring E170. Being the basis of chalk, it is used for writing on boards. It is used in everyday life for whitewashing ceilings, painting tree trunks, and for alkalizing the soil in gardening.

Mass production/use

Purified from foreign impurities, calcium carbonate is widely used in the paper and food industries, in the production of plastics, paints, rubber, household chemicals, and in construction. Paper manufacturers use calcium carbonate simultaneously as a bleaching agent, a filler (replacing expensive fibers and dyes), and a deoxidizing agent. Manufacturers of glassware, bottles, and fiberglass use calcium carbonate in huge quantities as a source of calcium - one of the main elements necessary for glass production. Widely used in the production of personal care products (such as toothpaste) and in the medical industry. In the food industry, it is often used as an anti-caking agent and separating agent in dry milk products. If consumed in excess of the recommended dose (1.5 g per day), it may cause milk-alkali syndrome (Burnett's syndrome). Recommended for diseases of bone tissue.
Plastic manufacturers are one of the main consumers of calcium carbonate (more than 50% of total consumption). Used as a filler and dye, calcium carbonate is necessary in the production of polyvinyl chloride (PVC), polyester fibers (crimplene, lavsan, etc.), polyolefins. Products made from these types of plastics are widespread - pipes, plumbing fixtures, tiles, tiles, linoleum, carpets, etc. Calcium carbonate makes up about 20% of the coloring pigment used in the production of paints.

Construction

Construction is another major consumer of calcium carbonate. Putties, various sealants - they all contain calcium carbonate in significant quantities. Also, calcium carbonate is an essential component in the production of household chemicals - plumbing cleaners, shoe polishes.
Calcium carbonate is also widely used in purification systems as a means of combating environmental pollution; with the help of calcium carbonate, the acid-base balance of the soil is restored.

Being in nature

Calcium carbonate is found in minerals in the form of polymorphs:

• Aragonite
• Calcite
• Vaterite (or μ-CaCO 3)

• Limestone
• Marble
• Travertine

Geology

Calcium carbonate is a common mineral. In nature, there are three polymorphs (minerals with the same chemical composition, but with different crystal structures): calcite, aragonite and vaterite (vaterite). Some rocks (limestone, chalk, marble, travertine and other calcareous tuffs) consist almost entirely of calcium carbonate with some impurities. Calcite is a stable polymorph of calcium carbonate and is found in a wide variety of geological environments: sedimentary, metamorphic and igneous rocks. About 10% of all sedimentary rocks are limestones, composed predominantly of calcite remains of shells of marine organisms. Aragonite is the second most stable polymorph of CaCO 3 and is mainly formed in the shells of mollusks and the skeletons of some other organisms. Aragonite can also form in inorganic processes, for example in karst caves or hydrothermal vents. Vaterite is the least stable variety of this carbonate, and very quickly turns into either calcite or aragonite in water. It is relatively rare in nature when its crystal structure is stabilized by certain impurities.

Manufacturing

The vast majority of calcium carbonate extracted from minerals is used industrially. Pure calcium carbonate (for example, for food production or pharmaceutical use) can be made from a pure source (usually marble). Alternatively, calcium carbonate can be prepared by calcination of calcium oxide. dissolves, forming an acidic salt - calcium bicarbonate Ca(HCO 3) 2: CaCO 3 + CO 2 + H 2 O → Ca(HCO 3) 2. The existence of precisely this reaction makes it possible to form stalactites, stalagmites and other beautiful forms, and indeed to develop karst in general. At 1500 °C, together with carbon, it forms calcium carbide and carbon monoxide (II) CaCO 3 + 4C → CaC 2 + 3CO.

Goal of the work: determine lime activity, slaking speed and temperature.

Basic Concepts

Construction pneumatic lime is a product obtained by burning calcium-magnesium rocks until the carbon dioxide is released as completely as possible. Lime is used in a mixture with various additives to produce various binders: lime-quartz, lime-slag, lime-clay, etc. Sand-lime bricks, silicate blocks, reinforced large-sized silicate parts and various other construction products are made from it.

The main process in the production of air lime is calcination, in which the limestone is decarbonized and converted and converted into lime by the following reaction:

CaCO 3 + 178.58 kJ →CaO + CO 2

In laboratory conditions, the dissociation of calcium carbonate occurs at approximately 900 °C; in production, the firing temperature is 1000-1200 °C.

Quicklime comes in lump and ground forms. It is obtained in the form of pieces of light yellow or gray color. It intensively absorbs moisture and therefore it is recommended to store it in a hermetically sealed state. If the raw material contains more than 6% clay impurities, then the calcined product exhibits hydraulic properties and is called hydraulic lime.

The quality of the resulting lime is assessed by activity, which shows the total content of free calcium and magnesium oxides in an active state. In addition to them, lime may contain oxides MgO and CaO in an inactive state; these are undecomposed carbonate and coarse-crystalline inclusions (burnout).

Depending on the content of active CaO and MgO, lime is produced in three grades (Table 9.1).

Table 9.1

Classification of lime by grade

Air lime can be used in slaked form.

Slaked lime comes in the form of fluff, dough or milk. The moisture content in the fluff does not exceed 5%, in the dough less than 45%. The quenching process proceeds according to the following scheme:

CaO + H 2 O ↔ Ca(OH) 2 +65.1 kJ

and is accompanied by the release of heat, which causes a rise in temperature that can ignite the tree. Hydration of calcium oxide is a reversible reaction, its direction depends on the temperature and pressure of water vapor in the environment. The elasticity of dissociation of Ca(OH) 2 into CaO and H 2 O reaches atmospheric pressure at 547 ° C; at higher temperatures, calcium hydroxide can partially decompose. In order for the process to go in the right direction, it is necessary to strive to increase the elasticity of water vapor over Ca(OH) 2 and not allow the temperature to be too high. At the same time, overcooling of slaking lime should be avoided, as this greatly slows down slaking. More than half of its grains have a size not exceeding 0.01 mm. Vaporization protects the material from excessive temperature rise.

The volume of fluff when slaking lime is 2-3 times greater than the volume of the original quicklime due to an increase in the volume of voids (pores) between the individual grains of the resulting material. The density of quicklime is on average 3200, and that of slaked lime is 2200 kg/m3.

To slak the lime, theoretically it is necessary to add 32.13% water by weight. Practically, depending on the composition of the lime, the degree of its firing and the slaking method, they take approximately two and sometimes three times more water, since under the influence of the heat released during slaking, vaporization occurs and part of the water is removed.

Depending on the temperature developed during quenching, a distinction is made between highly exothermic (t extinguishing >50 °C) and low exothermic (t extinguishing.<50 °C) известь, а по скорости гашения: быстрогасящуюся (не более 8 мин.), среднегасящуюся (8-25 мин.) и медленногасящуюся (более 25 мин.) известь.

To speed up the process of slaking lime, additives CaCl 2, NaCl, NaOH are used, which interact with calcium oxide to form more soluble compounds compared to Ca(OH) 2, and to slow it down, additives of surfactants, salts of sulfuric, phosphoric, oxalic, and carbonic acids are used.

Limestones (in the broad sense) have extremely diverse applications. They are used in the form of lump limestone, crushed stone, crushed sand, mineral powder, mineral wool, limestone flour. The main consumers are the cement industry (limestone, chalk and marl), construction (production of building lime, concrete, plaster, mortars; masonry of walls and foundations, metallurgy (limestone and dolomite - fluxes and refractories, processing of nepheline ores into alumina, cement and soda ), agriculture (limestone flour in agricultural technology and animal husbandry), food (especially sugar). In the Yantikovsky region, limestone is mined in quarries in the village of Yantikovo, Mozharki.

The area is known for its abundance of limestones; lime burning has been carried out here since time immemorial. In 1982, a lime quarry was opened on the left side of the Straw River. This is used to fertilize the soil of collective and state farms in our and other neighboring regions of the republic. The quarry produces 45 thousand tons of lime annually.

According to geologists, limestone deposits in the Mozharsky quarry are about 15 million tons, and in the Yantikovsky quarry - 5 million tons.

The program for the socio-economic development of the Yantikovsky district for 2007-2010 indicates the main tasks to increase the efficiency of use of the district's natural resources. The expected results of the implementation of the program are also given: budgetary security per capita will increase, the level of average monthly wages of workers in sectors of the economy will increase, additional jobs will appear to ensure effective employment of the population, and the volume of industrial output will increase.

The Yantikovsky district is part of a zone where the average living standard of the population is considered below the norm; 66.7% of the district's population is unemployed. The main problem in finding employment for unemployed and unemployed citizens in the region is the lack of jobs in enterprises and organizations in the region. In this regard, we propose to pay attention to the development of industrial production, in particular the production of crushed stone, cement, and sugar. And for the production of cement and sugar, natural raw materials must be of high quality. Therefore, the purpose of our work is: 1 To study the qualitative and quantitative composition of limestone from 2 quarries in the Yantikovsky district.

Limestone is a sedimentary rock composed predominantly of calcium carbonate - calcite. Due to its widespread occurrence, ease of processing and chemical properties, limestone is quarried and used to a greater extent than other rocks, second only to sand and gravel deposits. Limestones come in a variety of colors, including black, but the most common types are white, gray, or have a brownish tint. Bulk density 2.2–2.7. This is a soft breed that can be easily scratched by a knife blade. Limestones boil violently when interacting with dilute acid. In accordance with their sedimentary origin, they have a layered structure. Pure limestone consists only of calcite (rarely with a small amount of another form of calcium carbonate, aragonite). There are also impurities. The double carbonate of calcium and magnesium - dolomite - is usually found in variable quantities, and all transitions between limestone, dolomitic limestone and the dolomite rock are possible.

Although limestones can form in any freshwater or marine basin, the vast majority of these rocks are of marine origin. Sometimes they are deposited, like salt and gypsum, from the water of evaporating lakes and sea lagoons, but, apparently, most of the limestones were deposited in seas that did not experience intense drying. In all likelihood, the formation of most limestones began with the extraction of calcium carbonate from seawater by living organisms (to build shells and skeletons). These remains of dead organisms accumulate in abundance on the seabed. The most striking example of calcium carbonate accumulation is coral reefs. In some cases, individual shells are visible and recognizable in the limestone. As a result of wave activity and under the influence of sea currents, reefs are destroyed. Added to the limestone debris on the seabed is calcium carbonate, which precipitates from the calcium-saturated water. Calcite, coming from destroyed older limestones, also participates in the formation of younger limestones.

Limestones are found on almost all continents, with the exception of Australia. In Russia, limestones are common in the central regions of the European part, and are also common in the Caucasus, the Urals and Siberia.

1. 2 Cement

Cement is a binding powdery material that forms a plastic mass that can gradually harden into stone. It consists mainly of tricalcium silicate 3 CaO SiO2.

The composition of cement may include various additives; the mass ratio of oxides determines the technical suitability of the cement. Silica, which is part of it, binds calcium and aluminum oxides; in this case, the following silicate compounds are formed - 3CaO SiO2 nH2O, 2CaO SiO2 nH2O; hydroaluminates - 3CaO X AI2 O3 6H2O; aluminoferrites - 4CaO AI2 O3 Fe2O3.

The most common type of cement is Portland cement. It has great mechanical strength, stability in the air and under water, and frost resistance. The main raw materials for the production of Portland cement are limestone and clay containing silicon (IV) oxide.

Limestone and clay are thoroughly mixed and their mixture is fired in inclined cylindrical kilns, the length of which reaches more than 200 m, and in diameter - about 5 m. During the firing process, the kiln rotates slowly and the starting materials gradually move to its lower part to meet the hot gases - products combustion of incoming gaseous or solid pulverized fuel.

At elevated temperatures, complex chemical reactions occur between clay and limestone. The simplest of these are dehydration of kaolinite, decomposition of limestone and the formation of calcium silicates and aluminates:

Al2O3 2SiO2 2H2O → Al2O3 2SiO2 + 2H2O

CaCO3 → CaO + CO2

CaO + SiO2 → CaSiO3

The substances formed as a result of the reactions are sintered in the form of separate pieces. Once cooled, they are ground to a fine powder.

The hardening process of cement paste is explained by the fact that various silicates and aluminates that make up cement react with water to form a rocky mass. Depending on the composition, different types of cement are produced.

1. 3 Slaked lime. Calcium hydroxide is used to make sugar

Sugar beets are supplied to the plant by a hydraulic conveyor and, using pumps, are fed into the beet washing machine. The washed beets are lifted by an elevator 15-17 m and fed into a beet cutter, where they are crushed and turned into thin chips. Beet chips enter diffusion devices. The primary task of production is to more fully isolate sugar from beets. For this purpose, hot water is passed through diffusers to meet moving chips (beet pulp); the mass fraction of sucrose does not exceed 0.5%. Diffusion juice is an opaque dark liquid. The dark color is given by pigments that belong to nesasars.

And the task of another stage of production is to free the sucrose solution from impurities. To free the sucrose solution from impurities from above, lime milk is poured into it at the rate of 20-30 kg of calcium hydroxide Cu(OH)2 per 1 kg of beets. Under the influence of calcium hydroxide, the diffusion juice is neutralized.

Chapter 2. Experimental part of the work

2. 1 Determination of CaCO3 in limestone.

The simplest way to determine CaCO3 in limestone is to treat a certain portion of an average sample of limestone with an excess of a titrated solution of hydrochloric acid and the excess HCl that has not reacted with CaCO3 is subjected to back titration with a caustic alkali solution. Based on the amount of HCl used to decompose limestone, the CaCO3 content in limestone is calculated.

For analysis, a sample of the average sample of limestone (200 g) was ground in a mortar, passed through a 0.5 mm sieve, from which a new average sample of 40 g was taken. Then a sample of about 2 g was taken from this average sample, placed in a volumetric flask with a capacity of 500 ml, moistened with 5 milliliters of distilled water and carefully added 50 ml of 1.0-normal hydrochloric acid solution. After the release of carbon dioxide, 300 ml of distilled water and the contents of the flask were poured into the flask for 15 minutes. boiled (until CO2 emissions completely stopped). At the end of boiling, the solution was allowed to cool, distilled water was added to the flask to the mark, mixed and the precipitate was allowed to settle to the bottom of the flask. After this, 100 ml of a clear solution was pipetted from here, transferred to a 250 ml conical flask and titrated with a 0.1 normal solution of caustic alkali in the presence of 2 - 3 drops of methyl orange until a slightly yellow color of the solution appeared.

(a KHCl – bKш) 0.005*500*100

Where a is the number of milliliters of solution taken for titration; in this case a = 100 ml; b – the number of millimeters of 0.1-normal caustic alkali solution used for titration of excess HCl;

KHCl and Ksh - corrections for the normality of acid (KHCl) and alkalinity (Ksh);

0.005 – number of grams of CaCO3 corresponding to 1 ml of 1.0 – normal acid solution;

P – sample of limestone.

CaCO3+2HCl → CaCl2+CO2+H2O

2. 2 Characteristic and specific reactions of magnesium cations

There are currently no publicly available specific reactions to magnesium cations. Of the general analytical reactions, the most typical for them are: interaction with acidic sodium phosphate.

Formation of double magnesium phosphate - ammonium salt.

NH4OH is added to water containing magnesium salts until the formation of magnesium oxide hydrate precipitate stops:

MgCl2 + 2NH4OH = ↓Mg(OH)2 + 2NH4Cl2

Then a solution of ammonium chloride is added here until the resulting magnesium oxide hydrate is completely dissolved:

Mg(OH)2 + 2NH4Cl = MgCl2 + 2NH4OH

A diluted solution of Na2HPO4 is carefully added dropwise to the resulting ammonium solution of magnesium salt. In this case, small white crystals of MgNH4PO4 fall out of the solution, some of which, in the form of a barely noticeable film, seem to “creep” up the walls of the test tube. If an amorphous precipitate is formed under the action of Na2HPO4, a few drops of HCl are added to dissolve it, after which a Na2OH solution is added and MgNH4PO4 is precipitated again. The maximum concentration of cations discovered by this reaction is 1.2 mg/l.

Since the formation of white MgNH4PO4 crystals was not observed, this means the concentration of magnesium cations

2.3 Determination of pH

To characterize aqueous solutions of electrolytes, it is conventional to use the concentration of H+ ions. At the same time, for convenience, the value of this concentration is expressed through the so-called hydrogen index - pH.

The hydrogen index is the negative logarithm of the molar concentration of hydrogen ions in a solution: pH = -1g

In pure water, obviously, pH = 7. If the pH is 7, then the solution is alkaline.

The pH of aqueous solutions was determined with a universal indicator. The table shows the pH values ​​of aqueous solutions of limestone.

Results of the study of two quarries

Quarry deposit CaCO3 content MgCO3 content pH

S. Yantikovo 87% >9% 8.0-8.5

S. Mozharki 94.81%

1. Research shows that limestone from the Mozhar lime quarry contains 94.81% CaCO3 and 5.19% impurities.

2. The percentage of CaCO3 in limestone from the Mozharsky quarry turned out to be higher than in limestone from Yantikovsky.

3. Since the quality and composition of the limestone from the Mozharsky quarry is better, it meets the technological standards for cement production.

4. In the future, it is possible to build a sugar production plant in the Yantikovsky district.

Expected results

Budgetary security per capita will increase, the level of average monthly wages of workers in sectors of the economy will increase, additional jobs will appear that provide effective employment for the population, and the volume of industrial output will increase.

DEFINITION

Limestone– a rock of sedimentary origin, predominantly consisting of calcium carbonate in the form of calcite.

The chemical composition is expressed by the formula – CaCO 3. Molar mass – 100 g/mol.

Chemical properties of the main component of limestone - calcium carbonate

Calcium carbonate is a compound insoluble in water. When heated, it decomposes into its constituent oxides:

CaCO 3 = CaO + CO 2.

It dissolves in dilute acid solutions, resulting in the formation of unstable carbonic acid (H 2 CO 3), which instantly decomposes into carbon dioxide and water:

CaCO 3 + 2HCl dilute = CaCl 2 + CO 2 + H 2 O.

Calcium carbonate reacts with complex substances - acid oxides, salts, ammonia, etc.:

CaCO 3 + CO 2 + H 2 O ↔ Ca(HCO 3) 2;

CaCO 3 + SiO 2 = CaSiO 3 + CO 2 (t);

CaCO 3 + 2NH 3 = CaCN 2 + 3H 2 O (t);

CaCO 3 + 2NH 4 Cl conc = CaCl 2 + 2NH 3 + CO 2 + H 2 O (boiling);

CaCO 3 + H 2 S = CaS + H 2 O + CO 2 (t).

Among the reactions of calcium carbonate with simple substances, the most important is the reaction with carbon:

CaCO 3 + C = CaO + 2CO.

Physical properties of the main component of limestone - calcium carbonate

Calcium carbonate is white solid crystals, practically insoluble in water. Melting point – 1242C. Calcite, the mineral from which limestone is composed, has a trigonal crystalline structure.

Obtaining limestone

Limestone is a widespread sedimentary rock formed with the participation of living organisms in sea basins. The name of a variety of limestone reflects the presence in it of remains of rock-forming organisms, area of ​​distribution, structure (for example, oolitic limestones), impurities (ferruginous), nature of occurrence (limestone), geological age (Triassic).

Application of limestone

Limestone is widely used as a building material, and fine-grained varieties are used to create sculptures.

Examples of problem solving

EXAMPLE 1

EXAMPLE 2